Multijunction laser power converters are demonstrated for the first time with high efficiencies for average optical irradiances exceeding 150 W/cm2. The GaAs-based photovoltaic power converting III-V heterostructures are designed with six GaAs subcells having an area of 0.14 cm2, receiving up to 22 W of input power at ~811 nm, delivering over 14 W of output power. The maximum efficiencies are obtained in the range of 30 to 75 W/cm2, and efficiencies > 64% are still obtained at 160 W/cm2. The efficiency reduction for higher irradiance values originates predominantly from residual heat generated in the active layers. For example, in 100% duty factor measurements, the bandgap voltage offset saturates to Woc ~ 170 mV. However, in pulsed mode, Woc values as low as 150 mV have been obtained for a device base temperature of 20 °C. For smaller 0.029 cm2 devices, Woc values around 137 mV are obtained at 240 W/cm2.
Fafard et al. (Tue,) studied this question.